1. Field of the Invention
This invention relates to coating method and apparatus, and more particularly to a coating method and apparatus which are capable of pulverization-coating a fine material, such as the particles of fine powder.
2. Description of the Prior Art
In order to coat, for example, chemicals or food, a pan coating method, a fluidized bed coating method and a tumbling coating method are generally used.
However, the raw materials used in such coating systems are tablets, granules and pills, i.e. considerably large granular materials.
On the other hand, it has recently been demanded that, for example, chemicals having low solubility be pulverized in order to improve the solubility thereof.
However, there is a limit in the pulverization of such chemicals. Accordingly, the improvement of a dissolving rate of the pulverized chemicals is also limited. Under the circumstances, it is demanded that a dissolving rate of such pulverized chemicals be further improved.
The surfaces of particles of a certain kind of fine powder require to be modified, or contrary to the above-mentioned case, the particles of a certain kind of fine powder require to be coated with a material for reducing the solubility thereof.
Also, there are cases where the particles of, for example, the hydrophobic paint and pigment or the particles of fine wettable powder for agricultural chemicals require to be coated with a dispersing agent; and the particles of a copying toner and an active carbon require to be coated with a resin or wax.
When the particles of these fine materials are coated by the pan coating method, fluidized bed coating method and tumbling coating method, which are referred to previously, the granulation of the particles progresses simultaneously with the coating thereof. Therefore, it is very difficult to coat such fine particles while keeping the size thereof unchanged.
The techniques which enable the fine materials to be coated effectively for the above-mentioned purposes have not yet been proposed.